Image classes that derive form this class can be divided in two kinds: those that make the whole image available as const T* pointer, and those that load only a small portion of the image at a time in order to minimize RAM usage. This member function can be used to differentiate between the two: if the returned pointer is not NULL then it is a valid pointer to the whole image that can be used to draw the whole image in an optimized way. Otherwise the only way to get image data is to use getScanLine() to retrieve the image one scanline at a time. Note that getScanLine() always work for any kind of image.